The present invention generally relates to a physical quantity distribution sensing semiconductor device for reading, as electric signals, the distribution of a physical quantity that has been externally input and transduced into the electric signals. More particularly, the present invention relates to an amplifying solid-state imaging device for reading externally incident light as electric signals while eliminating variations resulting from the sensitivity components of the signals, and also relates to a method for driving the same.
In recent years, semiconductor devices for sensing a physical quantity distribution have been increasingly demanded. In particular, an amplifying solid-state imaging device, that is, a solid-state image sensor that can sense light among various types of physical quantities, attracts a great deal of attention, because such a device can operate with lower electric power and can easily integrate a variety of circuits on a chip.
Hereinafter, a conventional amplifying solid-state imaging device will be described with reference to the drawings.
FIG. 5 schematically illustrates an equivalent circuit corresponding to one pixel of a conventional amplifying solid-state imaging device. In FIG. 5, the reference numeral 100 denotes one of a plurality of pixels arranged in matrix. The pixel 100 includes: a photoelectric transducer 101, implemented as a photodiode to which an inverse bias voltage is applied, for transducing light into signal charges; a signal charge accumulator 102, implemented as a capacitor, for accumulating the signal charges transduced by the photoelectric transducer 101; a driving transistor 103 including an operation control section having the gate of a field effect transistor (hereinafter, abbreviated as xe2x80x9cFETxe2x80x9d) for controlling the drive current in accordance with the amount of the signal charges accumulated in the signal charge accumulator 102; a row select transistor 104 for selecting a pixel 100 on a specific row from a plurality of pixels 100; a column select transistor 105 for selecting a pixel 100 on a specific column from a plurality of pixels 100; and a resetting transistor 106 for reading the potential in the signal charge accumulator 102 at a predetermined time and then resetting the potential at an initial potential VDD. Herein, the capacitor constituting the signal charge accumulating section 102 is, in actuality, capacitance formed by the photoelectric transducer 101 and the gate of the driving transistor 103.
However, in the conventional amplifying solid-state imaging device, the driving transistor 103 is provided for each pixel 100 and the electrical characteristics of the respective driving transistors 103 are different from each other. Thus, an image of uniform quality is hard to obtain when the image is produced by using amplified signal current.
The noise components that has resulted from such a variation in electrical characteristics of the transistors and fixed in an image space, i.e., fixed pattern noise (FPN), can be roughly classified into the following two types.
The first type is noise components called xe2x80x9coffset componentsxe2x80x9d resulting from the variation in threshold voltages Vt of the FETs, for example. In such a case, even when light is uniformly incident onto an input section, unevenness is caused in the resulting image, because variation is found in the current values of the output signals.
The second type is noise components called xe2x80x9cdynamic sensitivity componentsxe2x80x9d resulting from the variation in capacitance of the signal charge accumulator 102 or in gains obtained by using the driving transistor 103 as a source follower.
FIG. 6 illustrates these two types of FPNs. In FIG. 6, the axis of abscissas indicates the quantity of light incident onto a pixel, while the axis of ordinates indicates the output values of each pixel. Line 111 represents the output characteristics of a pixel, while Line 112 represents the characteristics of another pixel. As shown in FIG. 6, a potential difference corresponding to the difference 113 between the Y intercepts is the offset component of the FPN. The offset component is generated because a drive voltage applied to the gate of the driving transistor 103 is obtained from the difference between a power supply voltage VDD and the threshold voltage Vt and because the threshold voltages Vt of the respective driving transistors are different from each other. On the other hand, the sensitivity component of the FPN is a ratio associated with each characteristic line. Specifically, in Line 111, the component is equal to: output/quantity of light=b1/a0, while in Line 112, the component is equal to: output/quantity of light=b2/a0. In this case, as can be easily understood from FIG. 6, the absolute value of the ratio b2/a0 of Line 112 is larger than that of the ratio b1/a0 of Line 111.
A solution for eliminating the offset component 113 is already disclosed in Japanese Laid-Open Publication No. 8181920.
However, no solution has ever been provided for the elimination of the FPN sensitivity component. As higher and higher image quality is sought after in the future, the adverse effects of the component on the image quality would presumably become more and more serious.
In view of the above-described conventional problems, the object of the present invention is to eliminate, from the FPN, the sensitivity components resulting from the variation in capacitance and the like of the charge accumulator.
In order to accomplish the object, according to the present invention, an output signal of each pixel is obtained by dividing a signal, which is output from a driving transistor in response to light incident upon a photoelectric transducer, by a reference output voltage, which is output from the driving transistor upon the application of a predetermined reference electric signal thereto.
A first amplifying solid-state imaging device according to the present invention includes: a plurality of photoelectric transducing means, each sensing externally incident light and transducing the sensed incident light into signal charges having a charge quantity corresponding to the incident light; a plurality of signal charge accumulating means, each accumulating the signal charges transduced by an associated one of the photoelectric transducing means; and signal reading means for sequentially reading out the signal charges, accumulated in the respective signal charge accumulating means, as electric signals. Each said electric signal is obtained by dividing an original electric signal by a reference electric signal and read out. The original electric signal is obtained by converting the signal charges accumulated in each said signal charge accumulating means. The reference electric signal is obtained by converting reference signal charges, which are output from each said signal charge accumulating means in response to predetermined reference light incident upon each said photoelectric transducing means, or by converting reference signal charges, which are output from each said signal charge accumulating means in response to a predetermined reference electric signal externally applied to each said signal charge accumulating means.
In the first amplifying solid-state imaging device, in the period of reading the electric signal, the original electric signal obtained by converting the signal charges accumulated in each said signal charge accumulating means that has received externally incident light is divided by the reference electric signal obtained by converting reference signal charges, which are output from each said signal charge accumulating means in response to predetermined reference light incident upon each said photoelectric transducing means, or by converting reference signal charges, which are output from each said signal charge accumulating means in response to a predetermined reference electric signal externally applied to each said signal charge accumulating means. And each division result is output as an electric signal. Thus, even if electrical characteristics of a plurality of photoelectric transducing means and a plurality of signal charge accumulating means are dynamically varied because of the incidence of light onto the respective photoelectric transducing means and respective signal charge accumulating means, it can be assumed that predetermined incident light has been uniformly input to every photoelectric transducing means and every signal charge accumulating means. As a result, the sensitivity components, resulting from the variation in sensitivities of the respective original electric signals that are output from the respective signal charge accumulating means, can be eliminated from the FPN.
The reasons why the predetermined incident light can be assumed to have been uniformly input to any of these means will be described later.
A second amplifying solid-state imaging device according to the present invention includes: an imaging area in which a plurality of unit pixels are arranged, each said unit pixel including photoelectric transducing means for sensing externally incident light and transducing the sensed incident light into signal charges having a charge quantity corresponding to the incident light, and signal charge accumulating means for accumulating the signal charges transduced by the photoelectric transducing means; a signal reading section for sequentially selecting a unit pixel from the unit pixels one by one and reading out the signal charges accumulated in the selected unit pixel as an electric signal; and a plurality of calibration sections formed between outputs of the imaging area and inputs of the signal reading section so as to correspond to the respective unit pixels in the imaging area. Each said calibration section includes: original signal storing means for storing an original electric signal obtained by converting the signal charges accumulated in one of the unit pixels associated with the calibration section; reference signal storing means for storing a reference electric signal that is output from the associated unit pixel upon the application of a predetermined reference electric signal to the associated unit pixel; and division means for dividing the original electric signal stored in the original signal storing means by the reference electric signal stored in the reference signal storing means and outputting the division result as an electric signal to the signal reading section.
In the second amplifying solid-state imaging device, each said calibration section includes: original signal storing means for storing an original electric signal obtained by converting the signal charges accumulated in one of the unit pixels associated with the calibration section; reference signal storing means for storing a reference electric signal that is output from the associated unit pixel upon the application of a predetermined reference electric signal to the associated unit pixel; and division means for dividing the original electric signal stored in the original signal storing means by the reference electric signal stored in the reference signal storing means and outputting the division result as an electric signal to the signal reading section. Thus, even if electrical characteristics of a plurality of unit pixels in the imaging area are dynamically varied because of the incidence of light onto the respective unit pixels, it can be assumed that predetermined incident light has been uniformly input to every unit pixel. As a result, the sensitivity components, resulting from the variation in sensitivities of the respective original electric signals that are output from the respective unit pixels, can be eliminated from the FPN, and the sensed incident light can be reproduced and output with high definition.
In the second amplifying solid-state imaging device, the original signal storing means preferably includes: an original signal holding capacitor; and an original signal switch transistor having a drain connected to the outputs of the imaging area, a source connected to one electrode of the original signal holding capacitor and a gate receiving an original-signal-calibrating signal. The reference signal storing means preferably includes: a reference signal holding capacitor; and a reference signal switch transistor having a drain connected to the outputs of the imaging area, a source connected to one electrode of the reference signal holding capacitor and a gate receiving a reference-signal-calibrating signal. The division means preferably includes a divider having a dividend input terminal connected to a common connection between the original signal switch transistor and the original signal holding capacitor, a divisor input terminal connected to a common connection between the reference signal switch transistor and the reference signal holding capacitor and an output terminal connected to the inputs of the signal reading section.
In such an embodiment, a calibration section for eliminating the FPN sensitivity components can be obtained with certainty.
In the second amplifying solid-state imaging device, each said calibration section preferably includes: an original signal offset component eliminator connected to the original signal storing means; and a reference signal offset component eliminator connected to the reference signal storing means. The original signal offset component eliminator preferably includes: a first no signal output holding capacitor; a no signal output switch transistor having a drain connected to the outputs of the imaging area, a source connected to one electrode of the first no signal output holding capacitor, and a gate receiving a no signal output calibrating signal; a first subtractor having a positive input terminal connected to a common connection between the original signal switch transistor and the original signal holding capacitor, and a negative input terminal connected to a common connection between the no signal output switch transistor and the first no signal output holding capacitor; and a corrected original signal holding capacitor connected in parallel between the first subtractor and the dividend input terminal of the divider. The reference signal offset component eliminator preferably includes: the no signal output switch transistor; a second no signal output holding capacitor having one electrode connected to the source of the no signal output switch transistor; a second subtractor having a positive input terminal connected to a common connection between the reference signal switch transistor and the reference signal holding capacitor, and a negative input terminal connected to a common connection between the no signal output switch transistor and the second no signal output holding capacitor; and a corrected reference signal holding capacitor connected in parallel between the second subtractor and the divisor input terminal of the divider.
In such an embodiment, since an original signal offset component eliminator connected to the original signal storing means and a reference signal offset component eliminator connected to the reference signal storing means are further provided, the FPN offset components can also be eliminated.
The method for driving an amplifying solid-state imaging device according to the present invention is a method for driving an amplifying solid-state imaging device including: an imaging area in which a plurality of unit pixels are arranged, each said unit pixel including photoelectric transducing means for sensing externally incident light and transducing the sensed incident light into signal charges having a charge quantity corresponding to the incident light, and signal charge accumulating means for accumulating the signal charges transduced by the photoelectric transducing means; a signal reading section for sequentially selecting a unit pixel from the unit pixels one by one and reading out the signal charges accumulated in the selected unit pixel as an electric signal; and a plurality of calibration sections formed between outputs of the imaging area and inputs of the signal reading section so as to correspond to the respective unit pixels in the imaging area. The method includes the steps of: making the signal reading section sequentially read out the signal charges, accumulated in the signal charge accumulating means of each said unit pixel, as an original electric signal; making one of the calibration sections, associated with the unit pixel, store the read-out original electric signal; making the signal reading section reset the read-out signal charges which have been accumulated in the signal charge accumulating means; applying a predetermined reference electric signal to the signal charge accumulating means accessed and making the calibration section store the reference electric signal that is output from the signal charge accumulating means to which the predetermined electric signal has been applied; and dividing the stored original electric signal by the stored reference electric signal and outputting the division result to the signal reading section as the electric signal.
In the method for driving an amplifying solid-state imaging device in accordance with the present invention, the signal charges accumulated in the signal charge accumulating means of each said unit pixel are sequentially read out as an original electric signal, and the read-out original electric signal is stored in each said calibration section. Then, the read-out signal charges accumulated in the signal charge accumulating means are reset, a predetermined reference electric signal is applied to the signal charge accumulating means accessed and the reference electric signal that is output from the signal charge accumulating means, to which the predetermined electric signal has been applied, is stored in the calibration section. Thereafter, the stored original electric signal is divided by the stored reference electric signal and the division result is output to the signal reading section as the electric signal. Thus, even if electrical characteristics of a plurality of unit pixels in the imaging area are dynamically varied because of the incidence of light onto the respective unit pixels, it can be assumed that predetermined incident light has been uniformly input to every unit pixel. As a result, the sensitivity components, resulting from the variation in sensitivities of the respective original electric signals that are output from the respective unit pixels, can be eliminated from the FPN.
A first physical quantity distribution sensing semiconductor device according to the present invention includes: a plurality of physical quantity sensing and transducing means, each sensing externally input physical quantity and transducing the sensed physical quantity into signal charges having a charge quantity corresponding to the physical quantity; a plurality of signal charge accumulating means, each accumulating the signal charges transduced by an associated one of the physical quantity sensing and transducing means; and signal reading means for sequentially reading out the signal charges accumulated in the respective signal charge accumulating means as electric signals. The electric signals are obtained by dividing an original electric signal by a reference electric signal and read out. The original electric signal is obtained by converting the signal charges accumulated in each said signal charge accumulating means. The reference electric signal is obtained by converting reference signal charges, which are output from each said signal charge accumulating means in response to predetermined reference physical quantity input to each said physical quantity sensing and transducing means, or by converting reference signal charges, which are output from each said signal charge accumulating means in response to a predetermined reference electric signal externally applied to each said signal charge accumulating means.
In the first physical quantity distribution sensing semiconductor device, in the period of reading the electric signal, the original electric signal, which is obtained by converting the signal charges accumulated in each said signal charge accumulating means that has externally received some physical quantity, is divided by the reference electric signal, which is obtained by converting reference signal charges that are output from each said signal charge accumulating means in response to predetermined reference physical quantity input to each said physical quantity sensing and transducing means or by converting reference signal charges that are output from each said signal charge accumulating means in response to a predetermined reference electric signal externally applied to each said signal charge accumulating means. And each division result is output as an electric signal. Thus, even if electrical characteristics of a plurality of physical quantity sensing and transducing means and a plurality of signal charge accumulating means are dynamically varied because of the reception of physical quantities by the respective physical quantity sensing and transducing means and respective signal charge accumulating means, it can be assumed that predetermined physical quantity has been uniformly input to every physical quantity sensing and transducing means and every signal charge accumulating means. As a result, the sensitivity components, resulting from the variation in sensitivities of the respective original electric signals that are output from the respective signal charge accumulating means, can be eliminated from the FPN.
A second physical quantity distribution sensing semiconductor device according to the present invention includes: a physical quantity distribution sensing area in which a plurality of unit sensing sections are arranged, each said unit sensing section including physical quantity sensing and transducing means for sensing externally input physical quantity and transducing the sensed physical quantity into signal charges having a charge quantity corresponding to the physical quantity, and signal charge accumulating means for accumulating the signal charges transduced by the physical quantity sensing and transducing means; a signal reading section for sequentially selecting a unit sensing section from the unit sensing sections one by one and reading out the signal charges accumulated in the selected unit sensing section as an electric signal; and a plurality of calibration sections formed between outputs of the physical quantity distribution sensing area and inputs of the signal reading section so as to correspond to the respective unit sensing sections in the physical quantity distribution sensing area. Each said calibration section includes: original signal storing means for storing an original electric signal obtained by converting the signal charges accumulated in one of the unit sensing sections associated with the calibration section; reference signal storing means for storing a reference electric signal, which is output from the associated unit sensing section upon the application of a predetermined reference electric signal to the associated unit sensing section; and division means for dividing the original electric signal stored in the original signal storing means by the reference electric signal stored in the reference signal storing means and outputting the division result as an electric signal to the signal reading section.
In the second physical quantity distribution sensing semiconductor device, each said calibration section includes: original signal storing means for storing an original electric signal obtained by converting the signal charges accumulated in one of the unit sensing sections associated with the calibration section; reference signal storing means for storing a reference electric signal, which is output from the associated unit sensing section upon the application of a predetermined reference electric signal to the associated unit sensing section; and division means for dividing the original electric signal stored in the original signal storing means by the reference electric signal stored in the reference signal storing means and outputting the division result as an electric signal to the signal reading section. Thus, even if electrical characteristics of a plurality of unit sensing sections in the physical quantity distribution sensing area are dynamically varied because of the reception of physical quantities by the respective unit sensing sections, it can be assumed that predetermined physical quantity has been uniformly input to every unit sensing section. As a result, the sensitivity components, resulting from the variation in sensitivities of the respective original electric signals that are output from the respective unit sensing sections, can be eliminated from the FPN, and the sensed physical quantity can be reproduced and output with high definition.
In the second physical quantity distribution sensing semiconductor device, the original signal storing means preferably includes: an original signal holding capacitor; and an original signal switch transistor having a drain connected to the outputs of the physical quantity distribution sensing area, a source connected to one electrode of the original signal holding capacitor and a gate receiving an original-signal-calibrating signal. The reference signal storing means preferably includes: a reference signal holding capacitor; and a reference signal switch transistor having a drain connected to the outputs of the physical quantity distribution sensing area, a source connected to one electrode of the reference signal holding capacitor and a gate receiving a reference-signal-calibrating signal. The division means preferably includes a divider having a dividend input terminal connected to a common connection between the original signal switch transistor and the original signal holding capacitor, a divisor input terminal connected to a common connection between the reference signal switch transistor and the reference signal holding capacitor, and an output terminal connected to the inputs of the signal reading section.